1. Field of the Invention
The present invention broadly relates to a parts transfer system for an integrated injection molding and blow molding system.
The key concept to this invention is that two groups of parisons in a single set of parisons arrive at the blow-molding unit in nearly the same condition. This is achieved by staggering the indexing of the table in order to enable different sections of the table to remain at different stations around the table for differing time intervals and/or by moving related sets of parisons from station to station in rapid succession to one another. With the staggered indexing of the table each set of parisons remains on the table for periods of time that are sufficiently similar to ensure that each set of parisons reaches the blow mold clamp in a similar condition. The movement of related sets of parisons within minimal separation intervals also enables related sets of parisons to arrive at a blow-molding unit in similar condition.
2. Summary of the Prior Art
U.S. Pat. No. 4,793,960 to Schad et al (incorporated herein by reference) describes a system for transferring parisons carried on pallets through conditioning stations before entering a finishing or blow molding station. In this system, all parisons from an injection cycle are transferred simultaneously to a plurality of pallets that are then fed sequentially to the blow molding station. With this system, each pallet carrying parisons remains in the transfer path for a different period of time thus requiring different temperature conditioning for each set of parisons on a pallet.
U.S. Pat. No. 5,753,279 to Takada et al (incorporated herein by reference) describes an injection stretch blow molding apparatus in which the array pitch of the preforms is changed so that the preforms can be blown in a blow mold. The patent does not disclose means for ensuring minimal temperature differential between parisons reaching the blow molding machine.
U.S. Pat. No. 5,744,176 to Takada et al (incorporated herein by reference) describes a parison transfer system where each parison travels through a heating section and a standby section before entering the blow molding section. The transfer system operates synchronously.
U.S. Pat. No. 5,902,612 to Ogihara (incorporated herein by reference) describes an injection stretch blow molding apparatus which includes an injection unit which forms a set of parisons during an injection cycle which is a multiple of the number of parisons that can be blown in a blow molding machine during each cycle. The transfer of parts from the injection molding machine to the blow molding machine is synchronous.
U.S. Pat. No. 4,310,282 to Spurr et al (incorporated herein by reference) describes a parison transfer system that has storage means for storing parisons while they are awaiting transfer to a blow molding station. The patent does not provide means for asynchronously transferring parisons so as to ensure their arrival at a blowing station in substantially the same condition.
U.S. Pat. No. 4,824,359 to Poehlsen (incorporated herein by reference) describes a parison transfer system that operates synchronously to transfer parisons from an injection molding station to a blow molding station.
U.S. Pat. No. 6,139,789 to Neter et al (incorporated herein by reference) describes a system for thermally conditioning each batch or set of parisons in a like manner by holding each batch in a separate conditioning unit. The patent does not suggest transporting the sets of parisons through transfer stations in a like manner.
U.S. Pat. No. 6,146,134 to Kresak et al (incorporated herein by reference) describes a transfer system for transferring parisons from an injection molding station to a blow molding station that includes adjustable temperature conditioning stations in the transfer path. The transfer table moves synchronously.
U.S. Pat. Nos. 5,501,589 and 5,578,262 to Marcus (each incorporated herein by reference) describe a transfer apparatus that uses an axially and laterally indexed platen to transfer the parisons. The system provides a multiple number of blow stations corresponding to the number of injection cavities in the injection-molding unit.
U.S. Pat. No. 5,509,796 to Settembrini (incorporated herein by reference) describes a preform transfer system where the preforms are blown into bottles. The preforms that have been held the longest on the transfer path are blown first. By blowing the bottles in reverse order to their travel time on the transfer system, the effects of variations in the characteristics of the preforms can be minimized.
U.S. Pat. No. 5,443,360 to Lamb et al (incorporated herein by reference) describes a synchronous transfer system for transferring a sub-multiple of the injection molded parisons to a blow molding machine during each molding cycle.
None of the prior art references address the problem of temperature deviation in separate sets of parisons arriving at the blow molding station. In some cases, the problem would not occur because there is a one-to-one correspondence between the injection molding unit and the blow-molding unit. In these cases, each parison is treated equally. In other cases, the temperature change in the parisons remains within an acceptable window during the transfer process and would not create a problem. In still other cases, the problem may not have been recognized and a certain amount of waste product was expected and accepted.
There are a number of problems and deficiencies with the known prior art devices. When transferring parts from an injection molding machine directly to a blow molding machine it is essential that the parts arrive at the blow molding machine in a uniform or similar condition. With injection molding machines that inject more than one group of parts at a time, the parts are sometimes delivered to the blow-molding machine with different temperature profiles. If these profiles are significantly different, the blown parts may have significantly different configurations. As the object is to create consistent parts, this is obviously unacceptable machine performance. In practice, it has been found that, for many parts, the temperature decay during transfer is acceptable and the parts still arrive at the blow-molding machine in sufficiently similar condition that the subsequently blown parts will be consistent with one another. However, this is not the case with all parts. In particular, parisons that require longer cycle times or are formed of particular materials, such as polypropylene that has a lower tolerance for temperature change, need to arrive at the blow molding station with little temperature variation. The present invention enables uniform blown parts to be generated for all types of parisons. The invention is achieved by enabling the parts transfer device to operate in a synchronous or asynchronous mode dependent on the character of the parison being created by the injection-molding machine.
The general aspect of the present invention is to provide an improved method and apparatus for transferring parts from an injection molding machine to a blow molding machine.
Another aspect of the present invention is to transfer parts from an injection molding machine to a blow molding machine where each part arrives at the blow molding machine in a substantially similar condition.
The foregoing aspects are achieved by providing a novel transfer system and method for transferring groups of parisons from an injection molding unit to a blow molding unit where the injection molding unit generates a plurality of groups of parisons simultaneously. The transfer mechanism transfers the parisons from the injection-molding unit to the blow-molding unit in such a way that each parison in each group of parisons is treated in a like manner. Each set of parisons is dropped from an arm of a robot attached to the injection-molding unit onto a transfer pallet on the transfer mechanism and transported to the blow-molding machine. The blow-molding machine is operated to receive and simultaneously blow each parison in each group of parisons with a minimal cycle time between blowing operations for each group of parisons from a single set of parisons. Each group of parisons is held in the transfer apparatus for an interval that is substantially the same for every group of parisons. This ensures that each individual parison arrives at the blow molding station in essentially the same condition.
The foregoing aspects are further achieved by providing a transfer table for an injection stretch blow mold system where the injection unit simultaneously injects a plurality of groups of parisons during an injection cycle and the blow molding unit blows a single group of blown articles during a blow molding cycle and the injection molding cycle is longer than the blow molding cycle by a factor which is greater than or equal to two. The transfer table includes means for indexing the transfer table through a plurality of stations.
The stations include a receiving station for receiving parisons from the injection unit, a blow station for blowing the parisons into blown articles, at least a first intermediate station between the injection station and the blow station and at least a second intermediate station between the blow station and the injection station, and means for operating the indexing means asynchronously to enable a pallet on the table to be held at a station for pre-selected intervals. The pre-selected intervals are selected so as to enable each group of parisons to remain in the at least first and second intermediate stations for an aggregate interval of time that is substantially equal for each group of parisons and to enable each group of parisons from a single injection cycle to be moved into the blow station in rapid succession.
The foregoing aspects are further achieved by providing, in an injection stretch blowing system comprising an injection unit for injecting a plurality of groups of parisons simultaneously, transfer means for transferring parisons to an index table a group at a time, an index table for transporting the transferred group of parisons through a plurality of stations and a blow molding machine at one of the stations, the blow molding machine simultaneously blowing a single group of the parisons into blown articles, the table being indexed at predetermined times and remaining stationary between the predetermined times, an improved parison transfer method comprising the steps of transferring a first group of parisons from a first injection cycle to the table immediately prior to indexing of said table, blowing, in the blow molding machine, a first group of parisons from another injection cycle into blown articles immediately prior to indexing of the table, transferring a second group of parisons from the first injection cycle to the table immediately after indexing of the table, and blowing, in the blow molding machine, a second group of parisons from the another injection cycle into blown articles immediately after indexing of the table.
Further objects and advantages of the present invention will appear hereinbelow.